Flat cathode ray tube traversed by tunnel containing magnetic deflector



ULFHYUH HUM/EM 313-+22w OR 393139970 SR April 11, 1967 w. R. AIKEN 3,

FLAT CATHODE RAY TUBE TRAVERSED BY TUNNEL CONTAINING MAGNETIC DEFLECTORFlled June 29, 1964 3 Sheets-Sheet 1 INVENTOR.

WILLIAM R. AIKEN Apnl 11', 1967 w. R- AIKEN 3,313,970

FLAT CATHODE RAY TUBE TRAVERSED BY TUNNEL CONTAINING MAGNETIC DEFLECTORFiled June 29, 1964 3 Sheets-Sheet 2 4 W 4 3104 5 4O /30b 22 0 o 29bApnl 11, 1967 AIKEN 3,313,970

FLAT CATHODE RAY TUBE TRAVERSED BY TUNNEL CONTAINING MAGNETIC DEFLECTORFiled June 29, 1964 3 Sheets-Sheet 3 United States Patent FLAT CATHODERAY TUBE TRAVERSED BY TUNNEL CONTG MAGNETIC DE- FLECTOR William R.Aiken, 10410 Magdalena Ave., Los Altos Hills, Calif. 94022 Filed June29, 1964, Ser. No. 378,540 6 Claims. ,(Cl. 31379) The present inventionrelates to the flat cathode ray tubes known as the Kaiser-Aiken typecathode ray tubes.

In tubes of this type the electron beam is usually delivered into thetube along a marginal edge thereof and a first set of electrostaticbeam-bending electrodes in combination with beam-accelerating andrefocussing electrodes in an area above said beam-bending electrodes isemployed to deflect the beam within a plane parallel to the targetsurface of the tube through an angle of ap proximately 90. In addition,a second set of electrostatic beam-bending electrodes is employed tobend the beam into a course approximately perpendicular to the targetplane for impingement upon the target surface. In view of the highvelocity of the electron beam as it leaves the beam emitting device, theinitial bending forces provided by said first set of beam-bendingelectrodes may be less than required to bend the beam through a full 90.This causes the raster produced upon the target surface by thetwice-bent beam, to be canted slightly with regard to the vertical. Inmy US. Patent No. 2,937,315 I have described a magnetic device forstraightening the raster produced upon the screens of cathode ray tubesof the type here under consideration. This device comprises a pair ofmagnet bars located adjacent to the front and rear faces of the tubeenvelope to establish a force field that passes through the envelope andimparts to the upwardly deflected electron beam an additional bendingmoment that straightens the raster upon the screen of the tube.

The diffieulty with magnetic raster-straightening devices of the typedescribed, is that the field established between the magnetic bars isnot uniform, and the force lines of said field are parallel only in theimmediate vicinity of a vertical center plane which divides the spacebetween the magnetic bars into symmetrical halves. At either side ofsaid plane of symmetry, the force lines above and below said plane archupwardly and downwardly, respectively. In flat tubes of the type hereunder consideration the electron beam is usually swept upwardly in avertical plane that lies closer to the side of the envelope where thesecondary deflection devices are located than to the target side of theenvelope where the phosphor screen is located. As a result thereof, whenusing a magnetic raster-straightening device of the type described theelectron beam is mostly acted upon by arched diverging portions, ratherthan straight and parallel portions of the force lines set up by themagnetic bars and is, therefore, bent to different degrees and indifferent directions in different regions of the envelope. This resultsin a defocussing of the beam in a plane parallel to the screen, and thisdefocussing of the beam is the more pronounced the higher is the levelat which the beam is bent into impingement with the phosphor screen ofthe tube by the secondary deflection electrodes.

An answer to the problem may be to space the magnetic bar on the rearwall of the envelope from the outer surface of the rear wall so that theplane of symmetry of the force field established by the magnetic barsmay coincide with the plane into which the electron beam is deflected bythe primary beam deflection electrodes. Such an arrangement, however,would detract from the main advantage of the flat tubes, i.e., theircompactness,

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and would significantly increase the power requirements for the magneticstructures.

The problems briefly outlined above in employing magnetic structures forstraightening the raster of flat cathode ray tubes of the type hereunder consideration, are greatly aggravated in tubes designed to producemulticolor pictures, such as the tubes which employ a pair ofsynchronized electron emitting devices arranged to produce tworegistering rasters upon phosphor screens that are applied to oppositesides of an intermediately positioned transparent target. In tubes ofthis type, the vertical planes into which the two electron beams aredeflected by the primary deflection devices would inherently intersectportions of the magnetic field established between the bars of aconventionally located magnetic straightening structure, that areremoved from the plane of symmetry of the field and wherein the forcelines are curved and diverge from each other.

The present invention aims to produce an improved arrangement forstraightening the raster produced upon the phosphor screen of a flatcathode ray tube of the type referred to, without introducing anysignificant defocussing of the beam as it is directed against thephosphor screen.

More particularly the present invention aims to provide a simple andelfective arrangement for straightening two registering rasters that areproduced upon opposite sides of a target plate to which differentphosphors are applied.

In the accompanying drawings FIGURE 1 is a fragmentary perspective of aflat twocolor cathode ray tube embodying the invention;

FIGURE 2 is a perspective of the envelope of said tube;

FIGURE 3 is a horizontal section through the same tube taken along line33 of FIGURE 4 and viewed in the direction of the arrows associated withsaid line;

FIGURE 4 is a vertical cross section through said tube taken along line4-4 of FIGURE 3 and viewed in the direction of the arrows associatedwith said line;

FIGURE 5 is a cross section, similar to FIGURE 4, of a modifiedembodiment of the invention;

FIGURE 6 is a horizontal section through the embodiment illustrated inFIGURE 5 taken along line 6-6 of FIGURE 6 and viewed in the direction ofthe arrows associated with said lines; and

FIGURE 7 is a cross section, similar to FIGURES 4 and 5, of yet anotherembodiment of the invention.

The embodiment of the invention illustrated in FIG- URES 1, 2, 3 and 4comprises an envelope 10 which may be of glass and which may be composedof two symmetrically shaped sections in the forms of shallow rectangulartrays and that are suitably fused together along their contacting edges(FIGURE 1). The envelope has two parallel flat side walls 12a and 12b,and suitably mounted within said envelope in the plane of symmetry ofits two sections is a transparent plate 18 which may likewise be ofglass. Applied to the opposite faces of said plate are layers ofdifferent type of phosphor 20a and 20]) that generate light of differentcolor in response to impingement by electrons. adjacent the side wallsthereof are relatively narrow channels 24a and 24b, respectively, ofrectangular cross section that extend parallel to the bottom edges ofthe phosphor screens 20a and 20b (FIGURE 4). In alignment with saidchannels the end wall 25 of the envelope 10 is provided with openings26a and 26b (FIGURE 2) into which are fused in an air tight manner thesockets 28a and 2812, respectively (FIGURE 1), of two electron beamgenerating devices. Located in the channels 24a and 24b are horizontalrows of adj acently positioned U-shaped deflection members 29a and 29b,respectively, which may be formed by metal strips or by coatings ofconductive Formed in the bottom of the envelope paint upon the floor andside walls of the channels 24a and 24b and which constitute the primarydeflection ele ments. Above the side bars of the U-shaped deflectionelements 29a, 29b, the side walls of the channels 240 and 24b form pairsof inwardly projecting shoulders and upon said shoulders are supportedpairs of longitudinally extending electrodes 30a and 30b that arecoextensive in length with the horizontal rows of deflection elements29a and 2%. Initially, a positive potential relative to the electronemitting electrode of the electron beam producing devices may be appliedfrom a suitable source to all the horizontal deflection members 290 and29b and to the electrode pairs 30a and 30b to produce a fieldfree regionalong which the electron beams may travel without interference in astraight line. During performance of the cathode ray tube, reduced, i.e.relatively negative potentials are successively applied to thedeflection members 2911 and 2% starting, for instance, with thehorizontal deflection members most remote from the electron emittingevices. These reduced potentials block travel of the electron in itsinitial direction to and beyond the members to which they are applied,and thus enable the pairs of positively charged electrodes 30a and 30bto accelerate the beams in an upward direction through the space betweenthe individual electrodes of each pair in planes parallel and adjacentto the side walls of the envelope 10, at points that lie progressivelycloser to the points of origin of said beams. Arrangements for sweepingthe electron beam of a flat cathode ray tube in this manner successivelyinto and across a plane parallel to its side walls and its phosphortarget in a direction substantially perpendicular to its initial courseare described in my US. Patents Nos. 2,864,970 and 2,928,014, to whichreference is made for details.

Above the hereinbefore described inwardly projecting shoulders, thesides of channel 24a and 24b carry additional superposed pairs ofelectrodes 31a, 32a and 31b, 32b, respectively (FIGURES 1 and 4), andduring performance of the tube suitable potentials are applied to theseelectrodes to refocus the deflected electron beams in two successivestages.

As best shown in FIGURE 4, the arrangement is such that the upwardlydeflected electron beams extend in planes that lie closely adjacent tothe inner surfaces of the side walls 12a and 12b of the envelope 10, andin any case closer to said side walls than to the phosphor screens uponthe centrally located target plate 18; and provided upon the inner facesof said side walls are arrays of vertically superposed, longitudinallyextending, deflection electrodes 34a and 34b that are preferably formedby layers of a transparent conductive varnish. Initially high positivepotentials are applied to the layers of phosphor 20a and 2012 upon theopposite faces of the target plate 18 and to all the superposed verticaldeflection electrodes 34a and 34b so that a field-free region is formedbetween the layers of phosphor and the oppositely located deflectionelectrodes, into which region the upwardly deflected electron beam maytravel without interference. As likewise explained in detail in thehereinbefore mentioned US. Patents Nos. 2,864,970 and 2,928,014, andalso in my US. Patent No. 2,904,722, during practical performance of thecathode ray tube, a voltage generating arrangement controlled by a syncdetection stage associated with the receiver, is arranged to apply anegative voltage first to the uppermost vertical deflection electrodesand successively to lower ones of said deflection electrodes for thetime required by the horizontal deflection elements to deflect theinitial beams successively in upward direction from one end to the otherend of the tube. Hence, the upwardly deflected beams are deflected intoimpingement with the positively charged layers of phosphor alongsuccessively lower levels and in this manner scan the phosphor layers onthe target from one side to the other and from top to bottom. It will beunderstood by those skilled in the art that the described deflectionprocess may be arranged to occur in the opposite direction, i.e., thepoten tials applied to the horizontal deflection electrodes may be suchthat the upward deflection of the beams proceeds from the horizontaldeflection electrodes nearest to the points of origin of the electronbeams toward the deflection electrodes most remote from said points oforigin, and the nature and order of application of the potentialssequentially applied to the vertical deflection electrodes may be suchthat the upwardly directed beams are first deflected into impingementwith their respective phoshor screens at their lowest levels and arethen deflected at successively higher levels.

As pointed out initially, the electrostatic deflecting force set up bythe horizontal deflection electrodes 29 is usually insufficient todeflect the initial beams upwardly by a full angle of due to the highinitial velocity of the electron beams, and the rasters appearing on thephosphor layers of the cathode ray tube may therefore be canted.Auxiliary deflection means in the form of magnetic bars located adjacentto the front and rear surfaces of the tube at the level of itsaccelerating and focusing electrodes 30, 31 and 32 are thereforenecessary to bend the initial beams by a full angle of 90 in an upwarddirection and thus straighten the rasters appearing on the phosphorscreens 20a and 20b of the tube. In order to subject the upwardlydeflected electron beams to the full force of the deflection fields setup by the vertical deflection electrodes, and to provide sufficientspace for the beams to bend into horizontal paths before impinging uponthe phosphor screens, it is desirable to place the vertical planes intowhich the initial beams are deflected as close as possible to thevertical deflection electrodes and in any case closer to said electrodesthan to the planes of the phosphor layers (FIGURE 4). Unfortunately,this places the upwardly deflected electrode beams into highly archedareas of the magnetic deflection field set up by and between the bars ofthe magnetic raster straightening structure and this is liable todefocus the beams and distort the raster appearing upon said layers inan unsightly manner.

In accordance with the invention I provide the envelope of cathode raytubes of the type referred to at the level of the accelerating andrefocussing electrodes with a tunnel or tunnels extending longitudinallythrough the tube from end face to end face (FIGURE 2) for the receptionof one or more of the field-establishing bars of the magnetic rasterstraightening structures. In this manner it is possible to locate thebars of a magnetic raster straightening structure in such a manner thatthe vertical plane of symmetry of the magnetic field established by andbetween said bars extends closely adjacent to the vertical beamdeflection electrodes. As a result thereof the beam is subjected toregions of the magnetic field wherein the force lines extendsubstantially parallel to each other and perpendicular to the plane intowhich the electron beam is deflected by the horizontal deflectionelements. While the tunnels may be made from glass and may in fact forman integral part of the envelope, they may also be made from othernon-magnetic materials, such as nonmagnetic metals. Thus, tubes ofnon-magnetic stainless steel may be arranged to extend between suitableapertures in the end walls of the envelope and may be fused to said endwalls along the edges of said apertures.

For the magnetic bars I prefer to use a material known as magneticrubber which is a synthetic or natural rubber compound into which alarge percentage, by weight, of particles of a magnetizable materialhave been worked. Upon energization bars made from magnetic rubber ofthis kind produce a highly uniform field, and bars made from thismaterial may readily be trimmed to influence the configuration andintensity of the field produced by and between them. As an alternative,bars of ceramic magnetic materials may be arranged at the proper placesin the interior of the envelope.

The envelope 10 illustrated in FIGURE 2 has a centrally located tubulartunnel 36 which extends above and intermediately of the openings 26a and26b for the sockets 28a and 28b, respectively, of the electron emittingdevices longitudinally from end face to end face of said envelope. Inthe assembled tube a bar 40 of magnetic rubber is received within thetunnel 36 and two additional bars 42a and 42b of magnetic rubber arelocated at either side of the envelope adjacent the outer surfacesthereof as shown in FIGURES 1, 3 and 4, where they maybe held in anysuitable manner, such as by means of cement. By properly orienting themagnetic bars 40, 42a and 42b relative to each other so that the outerbars present areas of opposite polarity to the oppositely located areasof the center bar 40, it is possible to establish separate magneticfields for the electron beams generated by the two electron beamemitting devices comprised in the tube and to center said fields withrespect to the vertical planes into which the electron beams aredeflected by the two sets of horizontal deflection members 29a and 29b.Thus, with an envelope constructed in accordance with my invention, itis possible to put a magnetic structure effectively into the interior,and in fact into the very center of a cathode ray tube without riskingimpairment of its magnetic properties during assembly of the tube whenthe envelope is subjected to elevated temperatures as its halves arefused together and as its interior is evacuated.

FIGURES 5 and 6 illustrate another embodiment of the invention designedto produce a two-color picture. In said embodiment the envelope 50 hasformed therein a longitudinal tunnel 52 of elliptic cross section thatis located below the target plate 54 which carries the differentphosphor layers 56a and 56b. Received within the tunnel 52 are twoseparate magnetic bars 58a and 58b, respectively, which cooperate withexternal magnet bars 60a and 60b located closely adjacent to the outersurfaces of the envelope to establish two separate auxiliary deflectionfields whose planes of symmetry coincide with the upwardly directeddeflection planes of the electron beams generated by the two electronbeam emitting devices comprised in the tube. To hold the bars 58a, 60aand 58b, 60b in their proper position relative to each other and toprovide a magnetic return path, circumferential straps or bands of steel62a and 62b, respectively, may be provided which embrace the outersurfaces of the external bars and the centrally located faces of theinternal bars, as shown in both FIGURES 5 and 6.

FIGURE 7 illustrates the manner in which the principles of the inventionmay be applied to flat cathode ray tubes employing but a single electronbeam emitting device and a single phosphor screen 63 that is applied tothe inner surface of the transparent picture area 64 of one of the sidewalls of the tube envelope 66. The envelope has but a single tunnel 68that extends longitudinally through the envelope from end face to endface thereof. The center axis of said tunnel 68 and hence the centeraxis of the magnetic bar 70 received within said tunnel is spaced fromthe vertical plane 71 into which the electron beam is deflected upwardlyby the horizontal deflection electrodes 72 by substantially the samedistance by which the center axis of the exteriorly located outer magnetbar 74 is spaced from the deflection plane of the electron beam.

While I have explained my invention with the aid of certain preferredembodiments thereof, it will be understood that the invention is notlimited to the specific constructional details shown and described byway of example, which may be departed from, without departing from.

the scope and spirit of the invention.

I claim:

1. A cathode ray tube comprising an envelope having relatively spacedside walls and a picture area, end walls extending between the end edgesof said side walls and defining an evacuated space with said side walls,and a tunnel in communication with the outside atmosphere extendingbetween opposite end walls at a level below said picture area;electrostatic means within said evacuated space below said picture areafor deflecting an electron beam upwardly into a plane parallel andadjacent to the inner surface of a side wall, and means passing throughsaid tunnel and externally adjacent to the outer surface of a side wallfor establishing a magnetic field passing through said evacuated space.

2. A cathode ray tube according to claim 1 wherein said magnetic fieldestablishing means are bars of magnetic rubber.

3. A two-color cathode ray tube comprising an envelope having relativelyspaced, substantially flat side walls, a transparent target platearranged in the space between said side walls and carrying differentphosphor layers upon opposite sides thereof, end walls extending betweenthe end edges of, and defining an evacuated space with said side wallsand a tunnel in communication with the outside atmosphere extendingbetween opposite ones of said end walls at a level below said phosphorlayers; electrostatic means within said evacuated space at either sideand below said target plate for deflecting electron beams upwardly intoplanes parallel and adjacent to the inner surfaces of said side walls,and means passing through said tunnel and externally adjacent to theouter surfaces of said side walls for establishing magnetic fieldspassing through said evacuated space with their planes of symmetrycoincident with said electron beam deflection planes to accentuate thedeflection of the electron beams.

4. A cathode ray tube according to claim 3 wherein said magnetic fieldestablishing means are bars of magnetic rubber.

5. A cathode ray tube comprising an envelope having relatively spacedsubstantially flat side walls and end walls extending between said sidewalls and adapted to define with said side walls an evacuated space, atarget plate mounted within said evacuated space in a positionsubstantially parallel to said side walls, electrostatic means withinsaid evacuated space at either side and below said target plate fordeflecting electron beams upwardly into planes parallel and adjacent tothe inner surfaces of said side walls, a magnetic bar arranged withinsaid evacuated space below said target plate intermediately of andparallel to said side walls, and magnetic bars arranged exteriorlyadjacent to said side Walls to establish magnetic fields passing throughsaid evacuated space.

6. A cathode ray tube comprising an envelope having relatively spacedside Walls and a picture area, end Walls extending between said sidewalls and defining an evacuated space with said side walls, and a tunnelin communication with the outside atmosphere extending between said endwalls at a level below said picture area; electrostatic means withinsaid evacuated space for deflecting an electron beam upwardly into aplane parallel and adjacent to the inner surface of one of said sidewalls, and magnetic means passing through said tunnel for establishing amagnetic field extending into said evacuated space.

References Cited by the Examiner UNITED STATES PATENTS 2,795,731 6/1957Aiken 313-92 2,850,669 9/1958 Geer 313-92 2,997,621 8/ 1961 Schlesinger31392 FOREIGN PATENTS 608,711 3/ 1962 Belgium.

JAMES W. LAWRENCE, Primary Examiner.

R. SEGAL, Assistant Examiner.

1. A CATHODE RAY TUBE COMPRISING AN ENVELOPE HAVING RELATIVELY SPACEDSIDE WALLS AND A PICTURE AREA, END WALLS EXTENDING BETWEEN THE END EDGESOF SAID SIDE WALLS AND DEFINING AN EVACUATED SPACED WITH SAID SIDEWALLS, AND A TUNNEL IN COMMUNICATION WITH THE OUTSIDE ATMOSPHEREEXTENDING BETWEEN OPPOSITE END WALLS AT A LEVEL BELOW SAID PICTURE AREA;ELECTROSTATIC MEANS WITHIN SAID EVACUATED SPACE BELOW SAID PICTURE AREAFOR DEFLECTING AN ELECTRON BEAM UPWARDLY INTO A PLANE PARALLEL ANDADJACENT TO THE INNER SURFACE OF A SIDE WALL, AND MEANS PASSING THROUGHSAID TUNNEL AND EXTERNALLY ADJACENT TO THE OUTER SURFACE OF A SIDE WALLFOR ESTABLISHING A MAGNETIC FIELD PASSING THROUGH SAID EVACUATED SPACE.